Polymers of isobutylene are well known. These relatively low molecular weight polymers range from slightly viscous oily liquids to very viscous liquids with a high degree of tackiness. Their uses include lube oil additive, electrical insulating oil, carrier for fertilizers, compressor lubricant and as additives for various adhesives, caulks and cosmetics. Polyisobutylenes are prepared commercially by the continuous polymerization of isobutylene contained in C.sub.2 -C.sub.5 petroleum mixture which usually contains other olefins. The isobutylene contained in such a gas mixture is preferentially polymerized by passing the liquified C.sub.2 -C.sub.5 feed through a reactor at a variably desired but constant temperature in the range of -40.degree. F. (-40.degree. C.) to +125.degree. F. (52.degree. C.) and a pressure of 0 to 150 psig (0 to 1034 kilopascals) in the presence of a catalyst. While a fixed bed catalyst can be employed, the preferred catalyst is finely divided aluminum chloride particles of critical particle size suspended in the liquified feed mixture passed through the reactor while simultaneously feeding a relatively smaller quantity of hydrogen chloride as a promoter or water, tert. butyl chloride or other substance which forms the promoter. After reaction, the reaction mixture is continuously removed, product polymer separated and purified, recovered catalyst and unreacted hydrocarbons recycled to the feed.
The polymerization reaction is highly exothermic. To complicate matters, maintaining a constant temperature during the reaction is a necessity as variations in reaction temperature will affect the molecular weight and viscosity of the polyisobutylene produced. Temperature control of such an exothermic, high flow rate, continuous reaction is exceedingly difficult. To accomplish this, prior art processes have employed some form of refrigeration of the reaction mixture. In U.S. Pat. No. 2,957,930 issued Oct. 25, 1960 to W. K. Jackson, a portion of the reaction zone mixture was continuously removed, cooled by refrigeration and returned to the reactor. In U.S. Pat. No. 3,119,884 issued Jan. 28, 1964 to J. R. Allen et al refrigerated cooling coils were placed in the upper vapor section of the reactor to cool and condense vapors formed during the reaction, the liquid condensate being returned to the reaction zone. While the prior art processes for controlling this exothermic reaction, as exemplified by the two previously mentioned patents, have proven to be successful from both a technical and commercial standpoint, the refrigeration systems required are extremely energy costly. It is the object of this invention to provide an improved, energy efficient means of controlling the reaction temperature in the continuous, liquid phase, catalytic polymerization of isobutylene. Other objects will become apparent from the description of the novel process contained herein.